Phase shifter utilizing variable delay imparted to circularly polarized electric waves by variably magnetized ferrite material



g- 1953 H. SCHARFMAN ETAL 0 PHASE SHIFTER UTILIZING VARIABLE DELAY IMPARTED TO CIRCULARLY POLARIZED ELECTRIC WAVES BY VARIABLY MAGNETIZED F ERRITE MATERIAL Filed May 31, 1957 5 W2 w w m%% N FA Q 2 5 .m c. a O m A 5 WW 0 m A V W 6 mm5 m 3M R 4 y 3 w/ m H 2 o 4 2 3 a r F United States Patent 3,100,287 PHASE SIHFTER UTILIZING VARIABLE DELAY IMPARTED TO CERCULARLY POLARIZED ELECTRIC WAVES BY VARIABLY MAGNE- TIZED FERRITE MATERIAL Howard Scharfman, Lexington, and Francis J. OHara,

Belmont, Mass, assignors to Raytheon Company, Lexington, Mass, a corporation of Delaware Filed May 31, 1957, Ser. No. 662,843 9 Claims. (Cl. 33324.1)

This invention relates to phase shifters, and more particularly, to adjustable phase-shifting devices of the nonreciprocal type capable of producing relatively large phase variations in energy traveling from a microwave source in an electromagnetic wave transmission system.

Variable phase shifters utilizing the Faraday rotation effect have been constructed which consist of a longitudinally-magnetized ferrite rod axially positioned within a conductive pipe or other waveguide structures and preceded and followed by circular polarizers. By means of such devices, a plane or linearly-polarized electromagnetic wave at microwave frequencies is converted to circular polarized energy in the first polarizer, is phase shifted in the ferrite section, and converted back to linear polarization in the output polarizer; the applied magnetic field strength usually being maintained below the value at which saturation or ferromagnetic resonance in the ferrite occurs. Thus, in such phase-shifting devices, the phase angle between the output electric vector of the electromagnetic wave and the input magnetic wave may be varied by shifting the phase of the energy passing through the ferrite element positioned within the Waveguide structure, depending upon the relative strength of the applied magnetic field and upon the length of ferrite material.

However, in applications in which a ferrite phase shifter of this type is used to introduce a desired phase shift, it is desirable in numerous applications to produce a relatively large value of phase shift for a given length of ferrite, and to have the input and output waveguide ports locate-d in relatively close proximity, such as, for example, in certain packaging applications where a minimum space is required between the input and output waveguide ports.

In accordance with the invention, a doubling of the phase shift for a given length of ferrite material and for a given applied ferrite field, which is equivalent to donbling the maximum phase shift before saturation of the ferrite material, is accomplished by feeding linearlypolarized microwave energy through a two-mode transducer or thruplexer, having a pair of polarizationselective side arms or connections in either a round or square waveguide, and thence into a conventional circular polarizer. The resultant circularly-polarized electrical energy from said polarizer is fed itno a ferrite phase shifter comprising a longitudinally-magnetized ferrite rod axially positioned in the waveguide and is thereby phase shifted proportional to the applied longitudinal field strength in the ferrite material. The energy emerging from the ferrite phase shift section is directed to a shorting plate or bar positioned at the end of the waveguide adjacent to the ferrite section, the sense of circular polarization of reflected electromagnetic wave energy being reversed by the shorting plate prior to reentering the ferrite phase shift section. The reflected wave moving back through the ferrite encounters a reversed longitudinal field so directed as to produce a second value of phase shift in the same electrical direction as the first, the phase shift being doubled on the second trip through the ferrite phase shifter. The circular polarizer then converts the circularly-polarized reflected wave energy back to a linearly-polarized wave in a plane orthogonal or crosspolarized to the input electromagnetic field, and in this manner, the side arm or second connection of the two-mode transducer may be used as the output of the phase-shifting device. It should be noted that this transmission-type phase-shifting device is nonreciprocal in the sense that a phase advance is realized for one direction of propagation, and .a delay is obtained for the other direction. Thus, a relatively large value of phase shift can be produced in a novel manner by introducing a first value of phase shift to microwave energy passing in one direction through the phase-shifting system and the same value of phase shift in magnitude and sign to energy traveling in the opposite direction of transmission therethrough. Moreover, the resultant value of phase shift, so produced, is capable of being con-trolled by varying the voltage applied to the ferrite phase shifter to obtain a nonreciprocal phase shift substantially proportional to the applied magnetic field.

The invention further discloses a modification of the above-described, cross-polarized phase shifter in which the input and output linearly-polarized magnetic fields are in the same plane, permitting the device having a single port to be used as an electrically-controllable short circuit. This can be achieved by replacing the two-mode transducer in the system with a fixed 45 ferrite Faraday rotator, or isolator, preceding the circular polarizer in the system. By adjusting the phase shift, the effective line length of the device may be changed. Thus, the device may be used as a shorting stub of variable length.

Other objects and advantages will be more readily perceived upon analysis of the drawing, in which:

FIG. 1 is an isometric view, partly in section, of the first embodiment of a phase shifter according to the invention;

FIG. 2 is .a graph showing the phase shift as a function of the strength of the applied magnetic field; and

FIG. 3 is a side view, partly in section, of a further embodiment of the invention.

Referring now to FIG. 1, a phase shift system is shown which includes a two-mode transducer 12, a circular polarizer 14, a ferrite phase shifter 16, and a shorting bar 18 positioned at the end of the waveguide adjacent to the ferrite phase shifter. As indicated, the ferrite phase shifter 16 is similar to the rotator section of the phase shifter disclosed in the co-pending application of Howard Scharfman, Serial No. 648,897, filed March 27, 1957, now United States Letters Patent No. 3,090,015, which issued May 14, 1963. More particularly, FIG. 1 shows .a rectangular input section of waveguide 20 having a flange 21 adapted to provide a connection with a microwave source of energy, such as a magnetron or klystron oscillator. The rectangular waveguide 20 will accept and support only TE waves in which the electric vector, which determines the plane of polarization of the wave, is parallel to the short side of the rectangular waveguide.

The two-mode transducer 12 is shown integral with the input section of waveguide and includes a rectangular output arm 23, .a flange 24 adapted to connect microwave energy to a load, and a second arm 25 co-operating with output arm 23 to provide a pair of conjugatelyrelated terminals or branches in that a wave launched in either one will not appear at the other. Therefore, microwave energy of the TE mode introduced into waveguide 20 will flow through the two-mode transducer 12 into the circular polarizer 14.

It should be understood that any standard type circular polarizer may be used, provided the proper polarization and mode of energy is thereby obtained. Moreover, it is obvious to one skilled in the art that a number of other well-known circular polarization means may be employed in lieu of the circular polarizerr14 as long as the length of the polarizer, and the structure within the section of waveguide is adapted to convert linearly-polarized energy to circularly-polarized energy. in the present instance, circular polarizer 14 comprises a section of circular waveguide 26 having a card or vane of dielectric material 27 diametrically positioned at 45 to the plane of the linearlypolarized input field within the circular waveguide for the distance necessary to convert the linearly-polarized field to a circularly-polarized held. The resultant circularlypolar-ized field is connected by means of output flange 28 to the ferrite phase shifter 16, which has the property of phase shifting the microwave energy transmitted therethrough in a direction which is dependent upon the direction of the applied axial magnetic field. More particularly, therefore, the phase shift through the ferrite phase shifter is described in detail in an article by Howard Scharfman entitled Three New Ferrite Phase Shifters, in the Proceedings of the I.R.E., vol. 44, pp. 1456-1459, October 1956.

The ferrite phase shifter 16, connected to the circular polarizer 14, includes a cylindrical ferrite element 32 positioned within the waveguide section 33 by means of a low-loss dielectric material 34 and 34a, such as Teflon, which acts as a solid-supporting medium for the ferrite element 32. The Teflon dielectric material may be cut to the inner diameter of the circular waveguide section 33, divided into two sections as shown at 35- in the region of the ferrite element, a hole bottom-drilled into each section, and the ferrite element slidably inserted into the Teflon. Many other methods for mounting the ferrite within the Teflon will suggest themselves to those skilled in the art. For example, when the Teflon is to be inserted into a curved section of the waveguide, the Teflon may be heated until soft and poured into that portion of the waveguide.

The ferrite device 16 further includes a magnetic fieldproduciug means, such as field coil 36, surrounding the circular waveguide 33 in the region of the ferrite element 32. The field coil may consist of 25,000 turns of wire connected to an alternating current source 3-7 of approximately 100 volts at a frequency of 10 kilocycles by way of leads 38 and 39.

As noted, the transmission phase shift through the ferrite rotator section is a function of the applied longitudinal field. Therefore, the phase shift can be expressed by the following equation:

5+ is equal to the phase constant of the circularly polarized wave rotating in the same sense as current causing the magnetic field;

B- is equal to the phase constant of the circularly-polarized wave rotating in the opposite sense of 6+; and

L is equal to the length of the ferrite rod.

FIG. 2 shows the variation of the phase as a function of the applied magnetic field for a typical X band microwave phase shifter. As the magnetic field is. increased, the phase shift increases slowly and then passes through an approximately linear region and finally saturates the ferrite element. In the present instance, a phase shift of from approximately zero degrees to 45 is obtained before the energy reaches the shorting plate or bar 18, which is soldered or otherwise connected to the end portion of the Teflon-filled circular waveguide section in the region of output flange 40. As shown in the diagrammatic representation of the path lengths followed by electrical energy traversing the phase shift system of FIG. 1, a vertically-polarized wave, shown at 41, is circularly-polarized by the circular polarizer 14 in the manner represented at 42, is phase shifted a predetermined number of degrees represented by the vector at 43, and reflected from shorting bar 40. The reflected wave moving back through the ferrite experiences a second phase shift of substantially the same value as the first phase shift, as represented at 44, and consequently, the phase shift is doubled on the second trip through the ferrite element. In this instance, the relative phase of the energy is shifted an additional 45 on the second trip.

It should be understood that, from examination of the curve shown in FIG. 2, the maximum variation of phase shift of the phase shifter 16 is a function of ferrite length, diameter, and saturation magnetization; therefore, an arbitrarily large electrically variable phase shift can be obtained by increasing the length of the device. However, phase variation up to :lOCrO can be obtained for use with applications requiring large linear phase variations with low constant insertion loss.

As noted, the reflected wave moving through the ferrite phase shifter reenters the circular polarizer 14 and is converted from a circularly-polarized reflected wave back to a linearly-polarized wave in a plane cross-polarized to the input field, as represented by the arrow 45 of FIG. 1. In this manner, the side arm 23 of the thruplexer 12 may be used as the output of the phase-shifting system. In this manner, the phase shift system is capable of producing greater phase variation per unit length than heretofore possible in conventional phase shift systems.

It should be understood that the ferrite phase shifter 16 can be constructed so as to have two planes of symmetry. It is possible, of course, to utilize a ferrite element of square outer configuration in conjunction with a circular waveguide or vice versa. It is also understood that the thruplexer 12 may consist of the waveguide of either square or circular cross-section as long as the dimensions of each side arm are chosen so that only the dominant mode in each can be propagated. It should be further understood that the length of the ferrite element 32 preferably exceeds that of its diameter so that the required magnetic field for a given angle of phase shift is held relatively low. It is also desirable to maintain the diameter of the ferrite rod less than /3 the diameter of the waveguide 33 for low-loss attenuation of the propagated wave. As noted, a square or circular waveguide struct-ure including symmetrical ridged guides in which the circularly-polarized waves of opposite sense have the same phase constant at zero field strength can be used as the propagation medium.

Referring now to FIG. 3, a modification of the single ferrite device of FIG. 1 is shown wherein a nonreciprocal 45 ferrite Faraday rotator of conventional design may be inserted between the circular polarizer'14- and the thruplexer 12, the side 23 of the thruplexer being terminated in a well-known matched termination 47, such as a section of waveguide filled with Polyiron, or any similar nonreflec-ting material adapted to absorb electrical energy. As shown, the 45 ferrite rotator 48 comprises a section of circular waveguide 49 filled with Teflon or similar dielectric material 29 and supporting a second ferrite element 50 axially positioned within the low loss dielectric material. A separate magnetic field-producing means 5' 1 surrounds the circular waveguide section 49 in the region of the ferrite element 50. This field-producing means may consist of a permanent magnet of suftficient strength to produce a nonreciprocal 45 rotation of the microwave energy passing through the ferrite material in the forward and reverse directions. This angular displacement of the linearly-polarized fields is represented by the arrows 52 and 53 in FIG. 3. In like manner, the input and output energy linearly-polarized in the same plane is represented by the arrows 41 and 55". Consequently, the device may be used as an electrically-controllable short circuit for well-known impedance matching applications.

While the shorting bar 18, as shown in FIGS. 1 and 3, is located a short distance from the ferrite element 32, it should be understood that at 'low frequency modulation of the ferrite, the field coil 36 may be located proximate or in contact with the shorting plate 18. This is possible because the eddy current effects produced in the shorting bar 18 (are negligible. However, at high modulation frequencies, the shorting bar is preferably positioned, as shown, a short distance from the field coil 36 and the ferrite element 32 to prevent eddy current losses from dissipating the driving field energy applied to the phase shifter. Also, a smaller field coil may be used to produce a specified phase shift using a given amount of field current when it is desired to produce a phase shift in energy waveforms having appreciable high frequency components. Furthermore, a direct current may be used to drive the field coil in either FIG. 1 or FIG. 3 to produce a constant phase shift of predetermined value, or a combination of direct current and alternating current may be applied to one or more field coils to produce a constant phase shift in connection with a variable phase shift.

For the foregoing reasons, it is to be understood that the above described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention. Moreover, the invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpreta-tion commensurate with the scope of the invention Within the art.

What is claimed is:

1. A phase-shifting system for producing a phase shift in substantially all of the electromagnetic wave energy traveling through a waveguide transmission line comprising a waveguide circular polarizer means for converting linearly-polarized wave energy to circularly-polarized wave energy, means for producing :a predetermined phase shift in said circularlypolarized wave energy passing through said phase-shifting means in a first direction, means reflecting substantially all said wave energy backward through said magnetic-field phase-shifting means in a direction opposite to said first direction, whereby an additional phase shift is introduced in said wave energy, means directing said phase-shifted magnetic Wave energy through said first recited waveguide means, thereby polarizing said phase-shifted wave energy in an orthogonal direction with respect to said wave energy traveling in said first direction, and polarization-selective means in the form of an orthogonal mode transducer for extracting substantially all of said orthogonally-polarized Wave energy from said system.

2. A phase-shifting device for electromagnetic wave energy comprising a section of waveguide adapted to receive and support electromagnetic energy in a plurality of linear polarizations, a pair of polarization-selective connections at one location along said waveguide each coupled to linearly-polarized wave energy at said location, one of said selective connections adapted to be connected to a load circuit, the other of said selective connections being connected to a circular polarizer adapted to convert linearly-polarized energy fed from said other connection to circularly polarized energy, a ferromagnetic element producing a phase shift of said circularlypolarized energy, and a reflecting member located at the end of said guide adjacent to said phase shift element to present a substantially short circuit to Wave energy incident upon said reflecting member, whereby substantially all of said energy is reflected back through said ferromagnetic element to the other of said selective connections.

3. A nonreciprocal phase-shifting device for electromagnetic wave energy comprising a section of circular Waveguide adapted to receive said electromagnetic energy, a pair of conjugate microwave connections coupled to one end of said guide adapted to support wave energy having fields polarized at right angles to each other, a circular polarizer including a second section of circular waveguide connected to one of said microwave connections containing a diametrically-disposed vane of dielectric material adapted to convert linearly-polarized wave energy from one of said conjugate microwave connections to circularly-polarized wave energy, ferrite element means positioned along the longitudinal axis of said section of waveguide, means encircling said ferrite element for providing phase shift of electromagnetic energy propagated in said ferrite element, and short circuit means connected to the output of said phase shift means for reflecting substantially all of said energy to the other of said conjugate microwave connections, whereby the phase shift of substantially all of said energy entering said device is doubled on the second trip through said ferrite element.

4. A phase-shifting system for producing a phase shift in substantially all of the electromagnetic Wave energy traveling through a waveguide transmission line comprising means for converting linearly-polarized wave energy to circularly-polarized wave energy, magnetic phase shift producing means for introducing a predetermined phase shift in said circularly-polarized wave energy passing through said magnetic phase-shift producing means in la first direction, means for reflecting substantially all said wave energy through said magnetic phase shift producing means in a direction opposite said first direction, thereby to produce a second phase shift in said wave energy, and orthogonal mode transducer means for extracting substantially all of said phase-shifted wave energy from said system.

5. A phase-shifting system for producing a phase shift in substantially all of the electromagnetic wave energy traveling through a Waveguide transmission line comprising an orthogonal mode transducer having first and second output arms, means connected to the first output arm of said transducer for converting linearly-polarized Wave energy to circularly-polarized wave energy, magnetic phase shift producing means including a waveguide section containing a longitudinally-magnetized ferrite element for introducing a predetermined phase shift in said circularly-polarized Wave energy passing through said ferrite element in a first direction, me ans for reflecting substantially all said wave energy through said fer-rite element in a direction opposite said first direction, thereby to produce a second phase shift in said wave energy, and means for extracting substantially all of said phase-shifted wave energy from the second output arm of said transducer, whereby substantially all of the energy entering said transducer is phase shifted.

6. A device for producing an electrical phase shift of substantially all of a polarized electromagnetic wave entering said device comprising a circular waveguide receptive of said electromagnetic wave, a circular polarizer for converting said electromagnetic wave from linear to circular polarization insaid waveguide, ferrite element means positioned along the longitudinal axis of said waveguide receptive of said circularly-polarized electromagnetic wave, means positioned in the region of said ferrite element for providing an axial magnetic field parallel to the direction of propagation of said electromagnetic Wave, and waveguide shorting means located adjacent said ferrite element for reflecting electromagnetic wave energy traversing said ferrite element back through said ferrite element.

7. A device for producing a variable electrical phase shift of a circularly-polarized electromagnetic wave comprising a circular polarizer, a circular waveguide connected to said circular polarizer and receptive of said circularly polarized electromagnetic wave, a ferrite element positioned along the longitudinal axis of said waveguide, a single field coil concentrically mounted along said waveguide in the region of said ferrite element, means for supplying an alternating current to said field coil to produce a phase shift in substantially'all ofsaidcircularly polarized energy: traversing said ferrite element in one direction to producea phase shift, waveguide shorting means reflecting said PhflSGc-Shiftfid energy back through said ferrite elementi-n another direction to produce double said first-produced phase shift and orthogonal transducer means for extracting said phase-shifted energy from said device.

8. A device for producing a variable electrical phase shift of substantially all of an electromagnetic wave comprising a circular polarizer receptive of said electromagnetic wave, a waveguide connected to said circular polarizer, a single ferrite element positioned along the longitudinai axis of saidwaveguide, a single field coil positioned in the region of said ferrite element, means for supplying a direct current to said field coil to produce a fixed phase shift in said circularly-polarized energy traversing said ferrite element in one direction to produce a phase shift, waveguide shorting means reflecting said phase-shifted energy back through said ferrite element in the reverse direction to produce double said first-produced phase shift and orthogonal transducer means for extract.- ing said phase-shifted energy from said device;

9. A device for producing a variable electrical phase shift of a circularly-polarized electromagnetic wave comprising a circular waveguide receptive of said electromagnetic wave, a circular polarizer connected to said circular waveguide, a section of waveguide connected to said circular polarizer, a ferrite element positioned along the longitudinal axis of said section of waveguide, a single field coil positioned in. the region of said ferrite element,

means f r s pp y n d t: cur and n al r at urrent to said fie d oilto. n o u s p 'am hif ai circularly polarized energy traversing said ferrite element in one directiomwaveguide shorting means reflecting said phase-shifted energy back through said ferrite element in the reverse direction to produce double said first-produced phase shift and orthogonal transducer means for extracting said phase-shifted energy from said device.

References Cited in the file of this patent UNITED STATES PATENTS 2,644,930 Luhrs July 7, 1953 2,760,166 Fox Aug. 21, 1956 2,767,389 Mumford Oct. 16, 1956 2,773,245 Goldstein etal. Dec. 4, 1956 2,787,765 Fox Apr. 2, 1957 2,830,289 Zaleski Apr. 8, 1958 2,832,054 Fox Apr. 22, 1958 2,857,574 Anderson Oct. 2-1, 1958 2,863,127 Albersheim Dec. 2, 1958 2,915,714 Wright et al. Dec. 1, 1959 3,058,049 OHara et 'al. Oct. 9, 1962 FOREIGN PATENTS Add. 64,770 France June 29, 1955 OTHER REFERENCES 

1. A PHASE-SHIFTING SYSTEM FOR PRODUCING A PHASE SHIFT IN SUBSTANTIALLY ALL OF THE ELECTROMAGNETIC WAVE ENERGY TRAVELLING THROUGH A WAVEGUIDE TRANSMISSION LINE COMPRISING A WAVEGUIDE CIRCULAR POLARIZER MEANS FOR CONVERTING LINEARLY-POLARIZED WAVE ENERGY TO CIRCILARLY-POLARIZED WAVE ENERGY, MEANS FOR PRODUCING A PREDETERMINED PHASE SHIFT IN SAID CIRCULARLY-POLARIZED WAVE ENERGY PASSING THROUGH SAID PHASE-SHIFTING MEANS IN A FIRST DIRECTION, MEANS REFLECTING SUBSTANTIALLY ALL SAID WAVE ENERGY BACKWARD THROUGH SAID MAGNETIC-FIELD PHASE-SHIFTING MEANS IN A DIRECTION OPPOSITE TO SAID FIRST DIRECTION, WHEREBY AN ADDITIONAL PHASE SHIFT IS INTRODUCED IN SAID WAVE ENERGY, MEANS DIRECTING SAID PHASE-SHIFTED MAGNETIC WAVE ENERGY THROUGH SAID FIRST RECITED WAVEGUIDE MEANS, THEREBY POLARIZING SAID PHASE-SHIFTED WAVE ENERGY IN AN ORTHOGONAL DIRECTION WITH RESPECT TO SAID WAVE ENERGY TRAVELLING IN SAID FIRST DIRECTION, A POLARIZATION-SELECTIVE MEANS IN THE FORM OF AN ORTHOGONAL MODE TRANSDUCER FOR EXTRACTING SUBSTANTIALLY ALL OF SAID OTHROGONALLY-POLARIZED WAVE ENERGY FROM SAID SYSTEM. 